1. Field of the Invention
The invention relates generally to the field of drilling and completion of multiple, highly inclined wellbores through subsurface rock formations. More specifically, the invention relates to methods for using a plurality of highly inclined wellbores to create a subsurface fracture network in a low permeability subsurface formation.
2. Background Art
Extraction of oil and/or gas from certain subsurface rock formations requires creating a network of wellbores extending laterally through the formation. The network of wellbores increases the effective drainage capacity. For certain low permeability formations, such as gas bearing shales, extending such networks of wellbores has made possible extraction of oil and/or gas from such formations to be commercially profitable.
FIG. 1 shows a plan view of an example multiple lateral wellbore network. Generally such a network is made by drilling a substantially vertical wellbore 4 from a convenient surface location. At a selected depth, the trajectory of the wellbore may be diverted from the surface location of the vertical wellbore, and then laterally (along the bedding planes of the target formations) into the target formation along a selected length. FIG. 1 shows three such wellbores 1, 2, 3 each originating from the vertical wellbore.
FIG. 1A shows the three lateral wellbores 1, 2, 3 after hydraulic fracture treatment thereof. At selected positions along each lateral wellbore 1, 2, 3, fracturing fluid containing proppant is pumped into each wellbore to create a permeable channel extending laterally outward from the wellbore. Fracturing also extends the effective drainage radius of each wellbore as a result of connecting the permeable channels to each wellbore.
A drawback to the multiple lateral wellbore network shown in FIGS. 1 and 1A is the risk of failure of one or more of the wellbores. Such failure may substantially reduce the production of oil and/or gas from the subsurface formation.